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Electric power steering apparatus

a technology of electric power steering and steering wheel, which is applied in the direction of steering initiation, instruments, vessel construction, etc., can solve the problems of abrupt decrease of steering assist power which acts in the positive steering direction, deterioration of convergence of steering wheel motion, etc., and achieves improved convergence of steering wheel during the return steering, improved stability of control, and improved steering wheel convergence

Active Publication Date: 2009-03-17
JTEKT CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0003]However, when the steering torque decreases abruptly as a result of the driver's hands being removed from the steering wheel or the like during the return steering, the steering assist power which acts in the positive steering direction also decreases abruptly. Accordingly, the following problem arises, that is, the return of the steering wheel to the straight-forward position becomes abrupt, and the convergence of the motion of the steering wheel deteriorates. It is an object of the present invention to provide an electric power steering apparatus that can solve such problems.
[0005]In the present invention, when the phase of the output signal of the torque sensor is altered by the phase control element, the gain in the higher frequency band in the frequency response characteristic of the output to input of the torque sensor is reduced in the return steering state in comparison to the positive steering state. As a result, even if the steering torque acting in the positive steering direction abruptly decreases during the return steering, the abrupt decrease in the basic assist torque corresponding to the detection value of the steering torque detected by the torque sensor can be suppressed. Accordingly, there is no abrupt variation in the steering assist power acting in the positive steering direction during the return steering, and the convergence of the steering wheel is improved.
[0007]As a result, when the assist gradient increases in the positive steering state, the phase margin in the open loop characteristic of the output to input of the torque sensor is increased, so that the stability of control can be improved.
[0008]According to the electric power steering apparatus of the present invention, the convergence of the steering wheel during the return steering can be improved, and the stability of control can be improved during the positive steering.

Problems solved by technology

However, when the steering torque decreases abruptly as a result of the driver's hands being removed from the steering wheel or the like during the return steering, the steering assist power which acts in the positive steering direction also decreases abruptly.
Accordingly, the following problem arises, that is, the return of the steering wheel to the straight-forward position becomes abrupt, and the convergence of the motion of the steering wheel deteriorates.

Method used

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Examples

Experimental program
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Effect test

first embodiment

[0016]The vehicle electric power steering apparatus 1 of the first embodiment shown in FIG. 1 comprises a mechanism for transmitting the rotation of the steering wheel 2 caused by steering operation to the vehicle wheels 3 so that the steering angle varies. In the present embodiment, the rotation of the steering wheel 2 is transmitted to a pinion 5 via a steering shaft 4, so that a rack 6 which engages with the pinion 5 is caused to move, and the movement of this rack 6 is transmitted to the vehicle wheels 3 via tie rods 7 and knuckle arms 8 so that the steering angle varies.

[0017]A motor 10 is provided to generate steering assist power which acts on the line via which the rotation of the steering wheel 2 is transmitted to the vehicle wheels 3. In the present embodiment, the rotation of the output shaft of the motor 10 is transmitted to the steering shaft 4 via a speed reduction gear mechanism 11, so that the steering assist power is applied.

[0018]The motor 10 is connected to a cont...

second embodiment

[0031]FIG. 7 shows the frequency response characteristic of the output to input of the torque sensor 22 in the The characteristic in the positive steering state in which the coefficient a1 is set as a is indicated by a solid line, the characteristics in the return steering state in which the coefficient a1 is set as β is indicated by a broken line, ω1=1 / (2πt1), ω2=1 / (2παt1), ω3=1 / (2πβt1), ω4=1 / (2πa2t2), and ω5=1 / (2πt2). Specifically, the phase control characteristic of the phase control element 162 is altered in accordance with the judgment result of the steering state judgment element 43g and the assist gradient R. As a result, the breakpoint frequency ω3 in the return steering state is set by the phase control element 162 so that this frequency is greater than the breakpoint frequency ω2 in the positive steering state. Accordingly, the gain of the output to input of the torque sensor 22 in the higher frequency band in the return steering state can be reduced to a lower value than...

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Abstract

In an electric power steering apparatus, a steering torque is detected by a torque sensor, and a motor which generates steering assist power is controlled so that steering assist power is generated in accordance with basic assist torque which corresponds to the detected steering torque. The phase of the output signal of the torque sensor is caused to vary by a phase control element. The phase control characteristic of the phase control element is altered in accordance with the judgment results of a steering state judgment element as to whether the steering state is a return steering state or positive steering state, so that, in the frequency response characteristic of the output to input of the torque sensor, the gain at the higher frequency band where the frequency is greater than a set value is reduced in the return steering state in comparison to the positive steering state.

Description

FIELD OF THE INVENTION[0001]The present invention relates to an electric power steering apparatus which provides a steering assist power by means of a motor.DESCRIPTION OF THE RELATED ART[0002]In an electric power steering apparatus, a method is used in which the relationship between the steering torque and basic assist torque is stored as assist characteristics, and a motor for generating steering assist power is controlled so that steering assist power is generated in accordance with basic assist torque which corresponds to the steering torque detected by a torque sensor. In the control of the motor, when the deviation between the target value of the motor driving current and the detection value of the motor driving current detected by a current sensor is reduced, the cut-off frequency of a low-pass filter through which the detection signal of the motor driving current passes is set to a larger value in a return steering state in which the steering wheel is steered in the directio...

Claims

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Application Information

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Patent Type & Authority Patents(United States)
IPC IPC(8): B62D5/04
CPCB62D5/0466
Inventor TAMAIZUMI, TERUTAKA
Owner JTEKT CORP